Hostile attributions are an important predictor of aggression in children, but few studies have measured hostile attributions as they occur in real‐time. The current study uses an interactive video racing game to measure hostile attributions while children played against a presumed peer. A sample of 75 children, ages 10–13, used nonverbal and verbal procedures to respond to ambiguous provocation by their opponent. Hostile attributions were significantly positively related to parent‐rated reactive aggression, when controlling for proactive aggression. Hostile attributions using a nonverbal response procedure were negatively related to proactive aggression, when controlling for reactive aggression. Results suggest hostile attributions in real‐time occur quickly and simultaneously with social interaction, which differs from the deliberative, controlled appraisals measured with vignette‐based instruments. The relation between real‐time hostile attributions and reactive aggression could be accounted for by the impulsive response style that is characteristic of reactive aggression, whereas children exhibiting proactive aggression may be more deliberate and intentional in their responding, resulting in a negative relation with real‐time hostile attributions. These findings can be used both to identify children at risk for aggression and to enhance preventive interventions. Aggr. Behav. 9999:XX–XX, 2014. © 2014 Wiley Periodicals, Inc.